Development Of Self-Humidifying Self-Breathing Micro-Proton Exchange Membrane Fuel Cells And Hydrogen Sources

The demand for power sources with superior performance has increased as a result of the rapid growth of the third generation (3G) mobile phone and portable electronics markets. Proton exchange membrane fuel cells (PEMFC) have been considered as one of the amazing power sources. In this paper, we focused on the development of a micro-PEMFC stack and hydrogen sources. The main researches include the contents below, the preparation and investigation of a novel self-humidifying membrane electrode assembly (MEA) structure, gas diffusion layer (GDL) carbonized using sucrose carbonization, development of a mini-type hydrogen generator and investigation of a micro-PEMFC .A novel self-humidifying membrane electrode assembly (MEA) with the active electrode region surrounded by an unactive"water transfer region (WTR)"was fabricated to achieve effective water management and high performance for PEMFCs. Polarization curves and power density curves of conventional and the self-humidifying MEAs were compared. The self-humidifying MEA showed maximum power density of 85 mW cm-2, which is twice higher than that of conventional MEA with cathode open. The effects of anode hydrogen flow rates, environmental temperature and relative humidity on the performance of the self-humidifying MEA were investigated. Then, the area of WTR was optimized. The performance of the self-humidifying MEA was compared with that of the conventional MEA with anode hydrogen humidified as different humidity. The results showed that the self-humidifying MEA exhibited better performance.Treatment of gas diffusion layers (GDLs) was proposed by sucrose carbonization. By this method, carbon was coated on the surface of carbon fiber homogeneously, resulting in the enhancement of carbon paper roughness, which improved the hydrophobicity of carbon paper with low PTFE loading. The sinterring temperature for sucrose carbonization was 400 oC with twice carbonization. The water contact angle of carbonized carbon paper with 10 % PTFE loading was measured as 137±1o at 25 oC, which was higher than 125±1o for non-carbonized carbon paper with the same PTFE loading. The electronic resistances of carbonized carbon papers with different PTFE loading were lower than those of non-carbonized carbon papers by 6 %-8 %. The MEA prepared by carbonized carbon paper with 10 % PTFE loading showed better performance compared to the other MEAs.A mini-type hydrogen generator with smart and simple design was fabricated. Aluminum was used as raw material to react with aqueous solution of sodium hydroxide, and produce pure hydrogen. The effects of sodium hydroxide concentration, dropping rate of the sodium hydroxide, and initial temperature of the solution on the hydrogen generation were analyzed. The results showed that the rate of hydrogen generation was increased with increase of the sodium hydroxide concentration, the dropping rate of sodium hydroxide, and initial solution temperature. The rate of hydrogen generation for sodium hydroxide solution with the concentration of 25 mass% and the dropping rate of 0.01 ml/min at 20 oC was nearly 38 ml/min. The polarization behavior and start-up performance of the single cell for the anode fueled with both the generator and the steel bottle were presented. The hydrogen utilization ratio can reach to 77 % proved by constant current experiment.Finally, a self-breathing micro-PEMFC stack with six cells for the structure of ladder form was developed. The hydrogen flowed in series inside the stack compulsively. The polarization performance, constant current and step current performance, start-up performance and long time operation of the stack were investigated. In order to improve the performance uniformity of the single cells, the structure of the stack was improved by combining with hydrogen generator, so that both of them were unitive. The improved stack showed more homogeneous performance. The maximum power of the improved stack was about 2.7 W. The using condition for the stack was investigated. Then, the linkage performance between the stack and hydrogen generator was tested under 300 mA and 700 mA, respectively.